1. Field of the Invention
The present invention relates to a lock for the roll-up door of a truck or other vehicle and more particularly to such a lock that includes a magnetically actuated latch movement preventing member.
2. Description of Prior Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Many vehicles, particularly trucks and trailers, have roll-up doors that permit entrance into the truck interior for the loading and unloading cargo. Locking devices of different types have been used to secure such roll-up doors in the closed position, to prevent unauthorized access to the truck interior. Locks of the type of the present invention are commonly used for that purpose.
The lock mechanism is situated in a heavy duty rectangular metal housing that is secured to the exterior surface of the truck door, adjacent the bottom of the door. The truck door jamb opposite the position of the lock has a recess into which a fixed part, in the form of a shaft or bar, is mounted. Within the lock housing is situated a latch mounted for rotation about an axis that extends through the housing, from the front wall of the housing to the rear wall. The latch includes a hook designed to engage the vehicle part recessed in the door jamb, when the latch is in the “closed” position.
A handle, accessible from the exterior of the housing, is connected to rotate the latch between the “closed” position, wherein the hook engages the vehicle part to secure the door to the jamb, and the “open” position where the hook is remote from the vehicle part, and the door is not secured. Also mounted within the housing is a key actuated lock cylinder. In a conventional lock of this type, the lock cylinder is rotated to permit a spring to move a member in a direction toward the front of the housing to intersect the path of the latch. In that forward position, the member blocks the rotational movement of the latch such that the hook is retained in engagement with the vehicle part in the door jamb.
In order to protect the lock, the lock cylinder is located within a strong cylindrical housing portion protruding from the front wall of the housing. However, like all locks, this type of lock can be attacked by thieves. If the perpetrator understands how the lock operates, an elongated tool, such as a screw driver, can be wedged through the key opening, along the side of the lock cylinder, and be used to push the latch movement preventing member toward the rear of lock, against the force of the spring. Moving the latch movement preventing member towards the rear wall of the lock, out of the path of movement of the latch, will defeat the lock. That is because it permits the latch to be rotated to disengage the hook from the door jamb, permitting the door to be opened.
In order to prevent this problem, and increase the security of the lock, the conventional lock was improved as described in U.S. Pat. No. 7,066,500, issued Jun. 27, 2006, which patent is incorporated herein by reference. The improved lock of the patent has a redesigned mechanism in which a spring biases the latch movement preventing member in the opposite direction, toward the rear of the lock housing, to the position in which it intersects the path of movement of the latch. With this modification, even if a tool is inserted into the housing, and beyond the lock cylinder, the latch movement preventing member cannot be pushed out of the path of the latch to permit the latch to rotate. That modification significantly enhances the protection that the lock provides, without increasing the cost or complexity of the lock.
The present invention is a further improvement of the lock in which the latch movement presenting member is magnetically actuated to move from a position out of the path of movement of the latch to a position intersecting the path of movement of the latch. The use of magnetic force to move the latch movement preventing member results in smoother and more reliable action as compared to that of a spring.
More specifically, the latch movement preventing member, which takes the form of a piston-like member, carries a permanent magnet. A second permanent magnet is carried on a mechanical linkage which is attached to the lock cylinder. When the key is used to lock the cylinder, the linkage moves to align the magnets. The magnets are oriented such that like polarity poles face each other and a strong repulsive magnetic force is created between the magnets. That force causes the member to move from its retracted position, against the force of a spring, to its extended position, blocking the rotation of the latch, and preventing the latch from disengaging the door jamb.
It is, therefore, a prime object of the present invention to provide a vehicle door lock with a magnetically actuated latch movement preventing member.
It is another object of the present invention to provide a vehicle door lock with a magnetically actuated latch movement preventing member which has a smoother and more positive action.
It is another object of the present invention to provide a vehicle door lock with a magnetically actuated latch movement preventing member which has improved reliability.
It is another object of the present invention to provide a vehicle door lock with a magnetically actuated latch movement preventing member in which the repulsive force between magnets causes the latch movement preventing member to move into the path of movement of the latch.